1. Field of the Invention
The present invention relates to a microscope capable of changing an illumination device in accordance with an observation method.
2. Related Background Art
There has been proposed a conventional microscope capable of observing a metallic sample or a wafer with a bright field observation or a dark field observation by changing from a bright field illumination unit to a dark field illumination unit (see Japanese Patent Application Laid-Open No. 2001-125002).
There has been another microscope capable of making a fluorescence observation of a biological sample such as cells or the like with different excitation light corresponding to each observing sample by selecting a filter cube corresponding to each kind of the observing sample.
In an observing sample such as a high molecule compound, a biomaterial and a semiconductor device, a demand on carrying out a fluorescence observation as well as a bright field observation and a dark field observation has recently been increasing. In order to meet the demand, there have been carried out various methods such as replacing a bright field illumination unit or a dark field illumination unit with a fluorescence illumination unit, superposing a fluorescence illumination unit upon a bright field illumination unit or a dark field illumination unit, and attaching a filter cube for a bright field or a dark field to a fluorescence illumination unit.
However, replacing an illumination unit is a troublesome task, and superposing illumination units causes problems that sufficient optical performance cannot be obtained, or it becomes difficult to observe since the eyepiece position becomes high.
Moreover, since a fluorescence illumination optical system is basically different from a bright field illumination optical system or a dark field illumination optical system, even if a filter cube for a bright field or a dark field is attached to a fluorescence illumination unit, optical performance of the illumination unit cannot compete with that of an illumination unit designed exclusively for a bright field illumination or a dark field illumination. For example, in an illumination unit for a bright field illumination or a dark field illumination, a UV-blocking filter for blocking harmful ultraviolet rays is put on the optical axis, or a diffuser for removing unevenness of the light source is put on the optical axis. On the other hand, in a fluorescence illumination unit, ultraviolet rays used for excitation light are scarcely removed. On the contrary, since brightness is important, even a diffuser which may cause reduction in brightness is not put on the optical axis.
As described above, in order that all kinds of observation such as a bright field observation, a dark field observation and a fluorescence observation can be carried out by a single illumination unit, when a bright field observation or a dark field observation is carried out, a UV-blocking filter for blocking ultraviolet rays and a diffuser are necessary to be put on the optical axis, and when a fluorescence observation is carried out, the UV-blocking filter and the diffuser are necessary to be removed from the optical axis.
Moreover, while upon carrying out a dark field observation, an aperture stop and a field stop have to be fully opened, upon carrying out a bright field observation, diameters of the aperture stop and the field stop have to be adjusted to the selected objective lens and the illumination condition.
As described above, the operation to change the observation method is troublesome. In addition, when the operation is mistaken, not only an observation image similar to the one obtained upon using an exclusively designed illumination unit cannot be obtained but also there is a danger that harmful ultraviolet rays or flash light cannot be removed.